The present invention relates to an engine system, more particularly, to a malfunction determining apparatus of engine system.
A typical vehicle engine system has a malfunction determining apparatus, or a self-testing apparatus, for determining a malfunction in the system. To improve the determination accuracy, the malfunction determining apparatus consecutively performs malfunction tests. If the apparatus detects a malfunction in a predetermined number of times of the test, the apparatus determines that the system is malfunctioning.
During a so-called short trip, in which the engine is stopped relatively early after being started, the malfunction test is performed only limited times. The engine may be stopped before the number of times of test in which a malfunction is detected reaches a predetermined number. Therefore, even if a malfunction is detected in each of consecutive short trips, the malfunction determining apparatus cannot determine a malfunctioning or determines a malfunctioning after a time lag. Particularly, in an engine system that performs so-called economy running, in which an engine is automatically stopped and restarted, each running time of the engine can be significantly short. Thus, the above disadvantage is pronounced.
Japanese Unexamined Patent Publication No. 7-36727 discloses an engine system that maintains the number of times of malfunction test in which a malfunction is detected. Specifically, the system of the publication maintains the number of detected malfunctions after the engine is stopped and accumulates the maintained number over several running periods. If short trips are repeated, a malfunction is reliably determined when the accumulated number of detected malfunctions reaches a predetermined number.
However, accumulating the number of detected malfunctions over several running periods may lower the accuracy of the malfunction determination. That is, erroneously detected malfunctions are counted as detected malfunctions even if the erroneous detection is relatively scarce and accidental. If the number of erroneously detected malfunctions is accumulated for an extended period and the number of detected malfunctions reaches a predetermined number, the system is erroneously determined to have a malfunction. Accordingly, the accuracy of the malfunction determination is lowered.
Accordingly, it is an objective of the present invention to provide a malfunction determining apparatus of an engine system that accurately determines a malfunction.
To achieve the foregoing and other objective and in accordance with the purpose of the present invention, an apparatus for determining the state of an engine system is provided. The apparatus includes a processing unit and a memory. The processing unit includes determining means, first counter means and second counter means. The detecting means detects whether there is a malfunction in the engine system every time a predetermined condition is satisfied. The first counter means generates a first counter value by counting the number of times when the detecting means detects a malfunction. The second counter means generates a second counter value for evaluating the reliability of the first counter value. The memory is connected to the processing unit and stores the first and second counter values regardless of whether the engine is stopped. The processing unit further includes determining means. The determining means evaluates the reliability of the first counter value based on the second counter value. When the first counter value is reliable and reaches a predetermined value, the determining means determines that there is a malfunction in the engine system.
The present invention may also be embodied in a method for determining the state of an engine system. The method includes detecting whether there is a malfunction in the engine system every time a predetermined condition is satisfied, generating a first counter value by counting the number of times when a malfunction is detected in the detecting step, generating a second counter value for evaluating the reliability of the first counter value, storing the first and second counter values in a memory, wherein the memory maintains the first and second counter values regardless of whether the engine is stopped, evaluating the reliability of the first counter value based on the second counter value, and determining that there is a malfunction in the engine system when the first counter value is reliable and reaches a predetermined value.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.